Refrigeration and Heat Pump systems

1. Refrigeration and Heat Pump systems P M V Subbarao Professor Mechanical Engineering Department I I T Delhi

2. A world that was present till the end of first decades of the 20th century. Only fresh foods that could be grown locally were available, and they had to be purchased and used on a daily basis. Meat was bought during the daily trip to the butcher's; the milkman made his rounds every morning. If you could afford weekly deliveries of ice blocks—harvested in the winter from frozen northern lakes—you could keep some perishable foods around for 2 or 3 days in an icebox. New York was a virtual ghost town in the summer months. Homes were built with natural cooling in mind. Ceilings were high, porches were deep and shaded, and windows were placed to take every possible advantage of cross-ventilation

3. A world that is present till the end of first decades of the 21st century. Fresh foods of all kinds were available just about anywhere in the country all year round. The milkman was all but gone and forgotten, and the butcher now did his work behind a counter at the supermarket. Indeed, many families concentrated the entire week's food shopping into one trip to the market, stocking the refrigerator with perishables that would last a week or more. New York is a busy town in the summer months. Buildings are totally isolated from fresh air.

4. Creation of Artificial Temperature/Quality

5. Performance Index

6. Reversed Carnot Cycle for Refrigerator and Heat Pump

7. Why not use the reversed Carnot refrigeration cycle? Easier to compress vapor only and not liquid-vapor mixture. Isothermal heat addition and rejection is impractical. Why don’t we reverse other power cycles?

8. Why not use the reversed Rankine cycle for Refrigeration ? Very costly to expand the liquid using a turbine? Cheaper to have irreversible expansion through an expansion valve.

9. The Vapor-Compression Refrigeration Cycle A reversed Rankine cycle with a modification can be used for refrigeration cycle. The most widely used refrigeration cycle is the vapor-compression refrigeration cycle. The vapor-compression refrigeration cycle has four components: Evaporator, compressor, condenser, and expansion (or throttle) valve. In an ideal vapor-compression refrigeration cycle, the refrigerant enters the compressor as a saturated vapor and is cooled to the saturated liquid state in the condenser. It is then throttled to the evaporator pressure and vaporizes as it absorbs heat from the refrigerated space.

10. Thermodynamics of Ideal VCR Cycle Ideal Vapor-Compression Refrigeration Cycle Process Description 1-2 Isentropic compression 2-3 Constant pressure heat rejection in the condenser 3-4 Throttling in an expansion valve 4-1 Constant pressure heat addition in the evaporator

14. Cascade refrigeration systems

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16. Multipurpose refrigeration systems

17. Gas Refrigeration Systems

18. Air Standard Refrigeration Cycle for Aircraft Cooling

19. Air Standard Cycle for Cryogenic Applications

20. Absorption Refrigeration Systems 

21. Thermoelectric Refrigeration Systems